Direct aging of a light metal casting alloy component

ABSTRACT

A method for heat treatment of a light metal casting alloy component includes, after demoulding at a demoulding temperature TE, bringing the light metal casting alloy component directly to an aging temperature TA above room temperature TR. Cooling of the light metal casting alloy component to the aging temperature TA proceeds with checking and regulation, and directly after cooling, the light metal casting alloy component is held at the aging temperature tA for a defined aging time TA.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit to European Patent Application No. 18 166 034.1, filed Apr. 6, 2018, which is incorporated by reference herein.

FIELD

The invention relates to a method for heat treatment of a light metal casting alloy component, preferably of a light metal casting alloy component produced by die casting, preferably with mechanical properties of R_(p0.2)≥120 MPa and an elongation at break A of over 5%.

BACKGROUND

During manufacture or the subsequent heat treatment of components consisting of aluminium alloys, in particular of die cast components, preferably for application in vehicle construction, the components must, as a rule, undergo heat treatment after casting in order to achieve necessary material properties.

For components made from aluminium-silicon alloys, which are intended to display particularly good hardness or strength, according to the prior art a solution treatment or reheating is applied for this purpose after casting and cooling of the component. In solution treatment, as many hardening alloy components as possible are dissolved in the solid solution. Hardening proper proceeds subsequent to the solution treatment by artificial aging at elevated temperatures of ≥150° C. In artificial aging, the alloy constituents which are less readily soluble as the temperature falls precipitate out again, which gives rise to the desired hardening effect.

DE 10 2008 046 803 A1 discloses a method for producing a cast component in which the cast component is subjected to solution treatment after the casting process and is then aged in a multistage process.

DE 10 2010 061 895 A1 discloses a method in which the cast component is brought to an annealing temperature and held there for a predetermined time and then quenched, wherein between the annealing and quenching intermediate cooling and aging take place, wherein after the intermediate cooling the cast component is reheated to the aging temperature and is held there for a predetermined period.

DE 10 2012 008 245 A1 discloses a method in which it is advantageous to subject the cast component to a solution treatment before aging. Aging then proceeds in two stages, wherein the first aging temperature is lower and the cast component is then brought to a higher aging temperature and is also held at this aging temperature for a given time.

SUMMARY

In an embodiment, the present invention provides a method for heat treatment of a light metal casting alloy component. The method includes, after demoulding at a demoulding temperature T_(E), bringing the light metal casting alloy component directly to an aging temperature T_(A) above room temperature T_(R). Cooling of the light metal casting alloy component to the aging temperature T_(A) proceeds with checking and regulation, and directly after cooling, the light metal casting alloy component is held at the aging temperature t_(A) for a defined aging time T_(A).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:

FIG. 1 is a time-temperature diagram for a method according to an embodiment of the invention for heat treatment of a light metal casting alloy component; and

FIG. 2 is a time-temperature diagram for a method according to an embodiment of the invention for heat treatment of a light metal casting alloy component with subsequent cathode dip-coating.

DETAILED DESCRIPTION

The heat treatment methods known from the prior art for achieving the required material properties have the disadvantage that, due to cooling to room temperature after demoulding and subsequent solution treatment, they require a high quantity of energy to be input again in order to implement the solution treatment after cooling to room temperature. These types of heat treatment are also very time-consuming.

Embodiments of the invention provide methods which improve energy input and time expended and enable comparable material properties to be achieved for light metal casting alloy components as for components which were subjected to heat treatments known from the prior art. Furthermore, embodiments of the invention reduce the process time for a light metal casting alloy component.

According to the invention, a light metal casting alloy component is brought, directly after demoulding at a demoulding temperature, to an aging temperature above room temperature, wherein cooling of the light metal casting alloy component to the aging temperature proceeds with checking and regulation, and wherein directly after cooling, the light metal casting alloy component is held at the aging temperature for a defined aging time.

According to an embodiment of the invention, a method for heat treatment of a light metal casting alloy component, preferably of a light metal casting alloy component produced by die casting, includes the following steps. Directly after demoulding, thus after the casting process, the light metal casting alloy component is brought to an aging temperature above room temperature. Complete cooling to room temperature at this point in time, as is known and conventional from the prior art, is dispensed with. Cooling of the light metal casting alloy component to aging temperature proceeds with checking and regulation, i.e. by establishing the component temperature, cooling intensity is accordingly regulated. Cooling is preferably constant. Checking of component temperature and corresponding regulation of cooling preferably proceeds at time intervals, or constant monitoring with constant regulation is also conceivable.

One advantageous configuration has also shown that, according to the invention, cooling to artificial aging temperature is assisted by a liquid medium, wherein this is applied to part or all of the light metal casting alloy component. This assists in achievement of the required material properties and, in the case of partial application of the liquid medium, in targeted regions having given material properties and the regions not cooled by means of the liquid medium having other properties or lower values.

Directly after demoulding and the subsequent checked and regulated cooling, the light metal casting alloy component is held at the aging temperature for a defined aging time. The light metal casting alloy component is then cooled to room temperature, wherein this is preferably performed using the ambient air.

The component temperature is preferably monitored during cooling and the cooling regulated accordingly, controlled cooling of the component thereby being achieved. Among other things, controlled cooling ensures that the required material properties are achieved which correspond to the properties of a component produced using a prior art method, these being achieved by heat treatment including a solution treatment and exhibiting mechanical properties of R_(p0.2)≥120 MPa and an elongation at break A of over 5%.

It is advantageous for the component temperature to be monitored optically or by means of contact with the light metal casting alloy component. Optical temperature measurement may be performed, for example, by means of a thermal imaging camera and contact measurement may be performed using heat sensors.

The light metal casting alloy components preferably do not undergo solution treatment, the advantage thereof being that only a small amount of energy has to be input to achieve the desired material properties since the desired material properties are achieved merely by checking and regulating cooling of the components to the aging temperature and holding the components at that temperature for a given time. In this way, at least one reheating operation is saved, which is accompanied by a reduction in energy and time.

According to a preferred embodiment, after demoulding the light metal casting alloy component is no longer heated or after demoulding the component undergoes no temperature increase, so enabling a reduction in energy since only sufficient energy has to be introduced to hold the component at temperature during aging.

A further configuration according to the invention lies in the fact that the light metal casting alloy component is brought to an aging temperature which lies between 80 and 280° C., preferably between 120 and 260° C.

It is advantageous for the light metal casting alloy component to be held at the aging temperature T_(A) for an aging time of 10 min. to 10 h, preferably for an aging time of 20 min. to 400 min., especially preferably for an aging time of 30 min. to 240 min. These time intervals and temperature ranges assist in the formation of the desired material properties.

Cooling to room temperature preferably takes place after aging using calm or moving air or using water, preferably a water bath. This allows the components to be stored in an exposed store or air circulation to be assisted by means of a fan.

According to the invention, it has proven advantageous for cooling to room temperature after aging to be assisted by a liquid medium, wherein this is applied to part or all of the light metal casting alloy component. This assists in achievement of the required material properties, and, in the case of partial application of the liquid medium, in targeted regions having given material properties and the regions not cooled by means of the liquid medium having other properties or lower values.

After cooling to room temperature, the light metal casting alloy component preferably undergoes a downstream surface finishing process, preferably a cathode dip-coating process, wherein this surface finishing process includes reheating, preferably by means of a furnace, and the aging time is reduced by the reheating time. In this way, the duration of the method may be reduced, the required material properties nevertheless being achieved. The aging time is thus reduced by the period over which the light metal casting alloy component undergoes the reheating of the downstream surface finishing process and the total duration of the method after demoulding of the light metal casting alloy component is not extended by a downstream process.

All possible configurations can be combined freely with one another.

The diagram shown in FIG. 1 is a time-temperature diagram for the method according to the invention for heat treatment of a light metal casting alloy component after demoulding of the light metal casting alloy component. After demoulding, the light metal casting alloy component, which has a demoulding temperature T_(E), is brought directly to an aging temperature T_(A), preferably by cooling, at which the light metal casting alloy component is aged for a time t_(A).

Cooling to the aging temperature T_(A) is checked and regulated, preferably by detecting the temperature of the component, wherein this may take place constantly or at time intervals, and accordingly regulating preferably active cooling on the basis of the measured component temperature. No solution treatment or other temperature increase takes place in the method according to the invention after demoulding and before the first cooling to room temperature. Directly after aging at a temperature T_(A), the light metal casting alloy component is cooled to room temperature T_(R), whereby the method according to the invention for heat treatment of a light metal casting alloy component extends over a period of t_(DA-Long).

FIG. 2 shows the method according to the invention in a time-temperature diagram in which, after cooling to room temperature T_(R) or performance of the method according to the invention for heat treatment of a light metal casting alloy component, a downstream surface finishing process takes place, preferably cathode coating, in which the light metal casting alloy component undergoes subsequent input of heat to a temperature T_(Warm) and is held there for a given time t_(Warm). As a result of a subsequent input of heat during the surface finishing process for the period t_(Warm), the duration of the aging t_(A) is accordingly reduced beforehand, whereby the duration t_(DA_Short) of the present heat treatment method is reduced, the material properties being achieved as required despite this reduction in aging t_(A) or corresponding to the values of a heat method known from the prior art involving solution treatment and also the method according to the invention for the period t_(A_Long).

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below.

The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

LIST OF REFERENCE CHARACTERS

-   T Temperature -   t Time -   T_(E) Component temperature after demoulding (around 280-350° C.) -   T_(A) Aging temperature (around 80-280° C.) -   T_(Warm) Temperature during reheating by the downstream surface     finishing process (around 200° C.) -   T_(R) Room temperature -   t_(A) Duration of aging (around 10 min.-10 h) -   t_(DA_Long) Duration of the method according to the invention     without subsequent downstream surface finishing process -   t_(DA_Short) Duration of the method according to the invention with     subsequent downstream surface finishing process -   t_(Warm) Duration of reheating by downstream surface finishing     process 

What is claimed is:
 1. A method for heat treatment of a light metal casting alloy component, the method comprising: after demoulding at a demoulding temperature T_(E), bringing the light metal casting alloy component directly to an aging temperature T_(A) above room temperature T_(R), wherein cooling of the light metal casting alloy component to the aging temperature T_(A) proceeds with checking and regulation, and wherein directly after cooling, the light metal casting alloy component is held at the aging temperature t_(A) for a defined aging time T_(A).
 2. The method according to claim 1, wherein the component temperature is monitored during cooling, and wherein the cooling is regulated accordingly.
 3. The method according to claim 1, wherein the component temperature is monitored optically or via contact with the light metal casting alloy component.
 4. The method according to claim 1, wherein the light metal casting alloy component does not undergo solution treatment.
 5. The method according to claim 1, wherein, after demoulding and prior to cooling to room temperature T_(R) or between demoulding and achievement of room temperature T_(R), the light metal casting alloy component is solely cooled or held at temperature.
 6. The method according to claim 1, wherein after demoulding and prior to cooling to room temperature T_(R) or between demoulding and achievement of room temperature T_(R), the light metal casting alloy component does not experience any further temperature increase.
 7. The method according to claim 1, wherein the light metal casting alloy component is brought to an aging temperature T_(A), wherein the aging temperature T_(A) lies between 80 and 280° C.
 8. The method according to claim 1, wherein the light metal casting alloy component is held at the aging temperature T_(A) for an aging time t_(A) of 10 min. to 10 h.
 9. The method according to claim 1, wherein cooling to room temperature T_(R) takes place after aging t_(A) using calm or moving air.
 10. The method according to claim 1, wherein cooling to room temperature T_(R) after aging t_(A) is assisted by a liquid medium, wherein the liquid medium is applied to part or all of the light metal casting alloy component.
 11. The method according to claim 1, wherein after cooling to room temperature T_(R), the light metal casting alloy component undergoes a surface finishing process, wherein the aging time t_(A) is reduced by the time t_(Warm) taken by the reheating for the surface finishing process.
 12. The method according to claim 1, wherein the surface finishing process takes the form of cathode dip-coating.
 13. The method according to claim 1, wherein the light metal alloy component is produced by die casting and has mechanical properties of R_(p0.2)≥120 MPa and an elongation at break A of over 5%.
 14. The method according to claim 7, wherein the aging temperature T_(A) lies between 120 and 260° C.
 15. The method according to claim 8, wherein the light metal casting alloy component is held at the aging temperature T_(A) for an aging time t_(A) of 20 min. to 400 min.
 16. The method according to claim 15, wherein the light metal casting alloy component is held at the aging temperature T_(A) for an aging time t_(A) of 30 min. to 240 min. 